Vertebrae are the individual irregular bones that make up the spinal column (aka ischis) a flexuous and flexible column. There are normally thirty-three vertebrae in humans, including the five that are fused to form the sacrum (the others are separated by intervertebral discs) and the four coccygeal bones which form the tailbone. The upper three regions comprise the remaining 24, and are grouped under the names cervical (7 vertebrae), thoracic (12 vertebrae) and lumbar (5 vertebrae), according to the regions they occupy. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished.
A typical vertebra consists of two essential parts: an anterior (front) segment, which is the vertebral body; and a posterior part—the vertebral (neural) arch—which encloses the vertebral foramen. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes, four articular, two transverse, and one spinous, the latter also being known as the neural spine.
When the vertebrae are articulated with each other, the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord), while between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels.
Conventional spinal spacer assemblies are used in spinal fusion procedures to repair damaged or incorrectly articulating vertebrae. Spinal fusion employs the use of spacer assemblies having a hollow mesh spacer tube and end caps that space apart and fuse together adjacent vertebrae. These mesh spacer tubes are often formed of titanium and are available in varying shapes and sizes. In addition, they can be trimmed on site by the surgeon to provide a better individual fit for each patient. Conventional spinal spacer assemblies come in different cross sections. These spacer assemblies are generally hollow and include openings in the side thereof to provide access for bone to grow and fuse within the mesh tube. The current intervertebral or interbody devices are designed using 3 major principles; the anatomical limitations of the surgical approach, optimization of bone graft volume to promote bony fusion, and optimization of the device contact with the vertebral endplates to resist subsidence. The current devices are generally static in that they cannot change shape or volume, thus they are limited by the anatomy and technique, and therefore they do not provide optimal bone graft volume or surface contact. The present invention attempts to solve these problems as well as others.